Unsymmetrical rectangular wave generator



@V- l 1949 l.. l.. LAKA-ros UNSYMMETRICAL RECTANGULAR WAVE GENERATORFiled JemY 29, 1944 Snventor ZM@ fw [faam Bu Cttorneg atented Nov. l,1949 UN SYMMETRICAL RECTANGULAR WAVE GENERATOR Louis L. Lakatos,Bala-Cynwyd, Pa., assigner to Radio Corporation of America, acorporation of Delaware Application January 29, 1944, Serial No. 520,247

(Cl. Z50- 27) 2 Claims.

This invention relates to a generator for the production of rectangularwaves, and in particular to a generator for the production ofunsymmetrical rectangular waves. In any one complete cycle, arectangular wave has two substantially horizontal portions, one in thepositive half of the cycle and the other in the negative half of thecycle. An unsymmetrical rectangular wave is a Wave in which these twohorizontal portions are of unequal length or duration.

Square or rectangular waves are applied to the deecting circuits ofcathode ray tubes in television equipment, range finders, and similarapparatus employing cathode ray tubes, and have many other applications.It is essential in many of such applications that the length or durationof the two respective horizontal portions of one cycle of such a Wave(at a given frequency) should be accurately fixed.

, Prior art devices for the production of waves having the featuresdescribed employ a plurality of tubes, often of the gaseous type, andconsequently they are expensive, occupy considerable space and requirecomplicated circuits for their proper operation. i

It is, therefore, an object of the invention to provide an improvedmethod of, and apparatus for, the production of unsymmetricalrectangular waves.

It is a further object of the invention to provide an improved methodof, and apparatus for, the production of rectangular waves, the lengthor duration of the respective horizontal portions whereof may beaccurately predetermined.

It is a further object of the invention to provide a simple, inexpensiveand compact circuit for the production of rectangular waves of thecharacter described.

A further object of the invention is to provide an improved rectangularwave generator which may be easily constructed, and which is stable inoperation.

In accordance with the invention, the rectangular wave is produced froma simple sine voltage wave. Two paths are provided for the sine wave,and the phase of the wave in one of such paths is shifted. The waves ineach path are then limited, amplified and again limited sothat eachassumes a substantially rectangular shape. The outputs of the two pathsare then added (in an algebraic sense), and this results in arectangular wave having two horizontal portions per cycle, the length orduration of such portions being determined by the amount of phase shiftoriginally provided in one of the paths or channels.

The invention may be better understood from the following description ofan embodiment thereof, when read in conjunction with the accompanyingdrawing, in which:

Figure 1 is a circuit diagram of a rectangular 2 wave generator inaccordance with the invention, and

Figures 2 to 9, inclusive, are graphs plotted on a horizontal time`base, which represent the shape of voltage waves at various points,more particularly described later, in the circuit of Figure 1.

Referring to Figure 1, a sine voltage wave is supplied by a generator40, which may include an oscillator, with or without one or more stagesof amplication. In the embodiment described, the sine wave may have afrequency of 200 cycles per second and an amplitude of 50 to 60 volts R.M. S. Two vchannels 6 and 8 are provided for this wave. One channel 6includes a capacitor l0, and the other channel 8 a capacitor Ill. Thevarious resistance and capacitance values of the elements of the circuitare indicated on the drawing in ohms and inicrcfarads, respectively.

As shown in the drawing, the capacitor I0 is connected to ground througha resistor l2, and to the grid 28 of a tube I8 through a resistor 54.Similarly, the capacitor i4 is connected to ground through a resistor I6and to the grid 32 of a tube 20 through a resistor 56. While the tubesi8 and 2B are shown in one envelope, they may be included in separateenvelopes.

The capacitance of the capacitor I4 is small by comparison with that ofthe capacitor lil. The difference between the impedances presented tothe wave in the respective channels results in a substantial phase shiftin the wave in the one channel 8, but a comparatively negligible phaseshift in the wave in the other channel 5. This effect is best seen froma comparison of Figs. 2, 3 and 4. Fig. 2 shows the shape of the waveproduced by the generator 40; Fig. 3 gives the shape of the wave whichhas passed through the capacitor IG, and shows that that capacitor hashad little effect onit; while Fig. 4 gives the shape of the wave whichhas passed through the capacitor I4, and shows the substantial phaseshift which has taken place in that wave lowing to the relatively highimpedance ci the capacitor to that of the parallel resistors I6 and 56.The resistors I2 and I6, in addtion to their function in procuring phaseshift (in combination with the capacitors I0 and I4, respectively), alsoprovides a path to ground for the current which flows in channels 6 and8, as hereinafter explained.

In one device, a twin triode, RCA type GSNIGT or GSL'ZGT, was used. Tubei8 has a cathode 22, an anode 24, and a control electrode or grid 2B.Tube 20 has a cathode 28, an anode 3D, and a control electrode or grid32. The anodes 24 and 30 are connected to a common B supply (not shown)through common resistors 36 and 38.

The voltage applied to the two anodes may be kept low-at say, 15 to 20voltsfor reasons which will appear hereinafter. If the device isincluded in equipment containing tubes whose anodes requre a highvoltage, the required voltage is ob tained by including the droppingresistor or bleeder 38 between the source 'of potential and the anoderesistor 36.

The grids 26 and 32, respectively, are maintained at zero bias; however,the comparatively large amplitude of the input Wave causes current toflow in the circuits which include these grids, and by reason of suchcurrent flow, the tubes develop self-biases.

On the positive half of the applied signal cycle, the grid currentscause the voltage applied to the grids in excess of the steady stategrid bias to be clipped, so that the tubes act as limiters. The shape ofthe voltage wave applied to the grids 26 and 32 is shown in Figs. 5 and6, respectively. The tubes amplify the signals applied to their gridsand invert their phase; since the anode voltages are low, limitingoccurs in the anode circuits as Well as the grid circuits, so that theoutput of the two tubes have the shapes shown in Figs. 7 and 8,respectively. These outputs are, however, combined or added in the anoderesistor 36 and take the shape shown in Fig. 9.

The portion of the wave shown in Fig. 9 which vr of the final outputwave is that Shown in Fig. 9

by the letters abcdefghz'.

The comparative lengths of the horizontal portions of the output wave inany one cycle depend on the relative phase shift in the two channels 6and 8. With the constants shown, a phase shift of approximately 65 maybe obtained, resulting in a ratio of 1:2 for the comparative lengths ofportions cd and ef in Fig. 9.

The capacitor lll causes negligible phase shift in the wave passingthrough channel 6; and, therefore, if this capacitor were omitted fromthe circuit, the omission would not substantially affect the relativephase shift of the waves in the two channels 6 and 8. Since it is thisrelative phase shift which determines the length of the two horizontalportions of the output wave, the capacitor l0 may, if desired, beomitted.

Certain other alternatives to the preferred embodiment will suggestthemselves to those skilled in the art. For example, the invention hasbeen described with a sine Wave as the input, and this is probably themost practical; but any periodic wave, for example, a square wave, maybe used for this purpose. Since, however, a square wave is rich inharmonics it should be borne in mind that in channel 6 (the channelinwhich comparatively negligible phase shift occurs) the reactance of thecondenser I0, at the fundamental frequency of the input wave, should besmall by comparison with the resistance of the parallel resistors I2 and54 in that channel.

A further alternative within the scope of the invention lies in thereplacement of the triodes i3 and 20 by tetrodes or pentodes. Suchmultielectrode tubes may be used where better control is desired, orwhere it is not desired to use an input wave with as large an amplitudeas before described.

While an input frequency of 200 cycles per second is often a useful onefor the purposes before mentioned, other frequencies may be employed ifdesired. The circuit illustrated will operate with satisfaction throughthe whole range of audio frequencies, down to as low as I0 cycles persecond; and, in the other direction, beyond the audio range up to 30 to40 kilocycles per second, at which frequencies tube capacities may beginto interfere with the proper operation of the circuit. By thesubstitution of pentodes for the tubes I8 and 20, higher frequencies maybe employed.

Similarly, the invention is not intended to be restricted to anamplitude of to 60 volts R. M. S. for the input signal. Very low voltageamplitudes may be employed if desired, although pentodes should then beused in place of the triodes I8 and 20, as explained before; the circuitwill also work satisfactorily at high input amplitudes, up to the pointwhere voltage breakdown occurs.

There has thus been described a method for the production of rectangularWaves, the respective horizontal portions of which may be accuratelypredetermined; the method employing simple, inexpensive and compactapparatus, and a circuit which is extremely stable in operation.

What I claim is:

1. An unsymmetrical rectangular wave generator, comprising incombination a pair of vacuum tubes, each of said tubes having at leastone electrode in addition to a cathode and an anode; a common source ofpotential for the anodes of said tubes, said potential beingsufficiently low to enable plate current to be cut off at a low negativegrid voltage; a common impedance connecting said source of potential tosaid anodes; a source of periodic wave voltage; and a pair of channelsconnecting said source of periodic Wave voltage to said controlelectrodes, each of said channels including a resistor and capacitor,the impedance of the capacitor in one of said channels relatively tothat of the resistor in the same channel being different from theimpedance of the capacitor in the other of said channels relatively tothat of the resistor in said other channel.

2. A circuit for converting a sine voltage Wave into an unsymmetricalrectangular wave, comprising in combination two channels for said sineWave, one of said channels including means for altering the phase of theWave passing therethrough, each of said channels including only oneREFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,223,840 Wolff Dec. 3, 19402,226,459 Bingley Dec. 24, 1940 FOREIGN PATENTS Number Country Date117,784 Australia 1943

